In the twenty-first century, a century of a science and technology revolution and a rise of environmental awareness, for responding to the rapid evolution of the new generation technology and the green energy products, the requirements and demands for the consumers are also grown, for example, portable 3C products such as mobile phones, personal digital assistant devices, smart phones, notebooks, tablet computers, digital cameras, and transportation such as electric vehicles, hybrid electric vehicles. Among various applications, better performance in terms of the electrical/energy capacity, the endurance life and the output power of the energy storage device are becoming more stringent. To reach the requirement, the design of the energy storage devices needs to be reconsidered. Taking lithium-ion battery as the example, graphite, the choice of negative electrode materials of commercial Li-ion batteries, is able to deliver capacity of 372 mAh g−1. The fair capacity with good stability makes it widely applied in 3C electronic products. With the size of the new electronic products goes smaller as well as fulfilling other new applications, Li-ion battery of higher energy density is continuously needed. Obviously graphite no longer satisfies the high-energy-density Li-ion batteries. Therefore high-capacity negative electrode materials like tin (Sn: 998 mAh/g, SnO2: 780 mAh/g) and silicon (4200 mAh/g), able to form alloys with Li, have been investigated for possible replacement of graphite. However, the alloying and de-alloying of the materials with Li during charging and discharging process accompany with drastic volumetric changes, leading to serious breaking/peeling off from current collector of the electrode of Li-ion battery, which is the biggest challenge for bringing into commercialization.
In order to solve or mitigate the drawback mentioning above, there are many methods disclosed in the references and patents. For example, U.S. Pat. No. 6,143,448 (Apr. 15, 1999) discloses a method of using metal salts as the precursor to synthesize a porous high-surface-area electrode material via evaporative drying heating. The synthesized porous material is able to accommodate the volume expansion during charging/discharging process. However, the high surface area electrode material is not suitable for certain electrochemical applications, especially the negative electrode of the lithium ion secondary battery. The method can only have 40-60% active Sn in the synthesized composite materials. Furthermore, the process employs tin-based compounds like tin chloride and tine sulfate, which is not environmental friendly.
U.S. Pat. No. 6,103,393 (Aug. 27, 1998) discloses a method to produce a carbon aerogel/metal composite material. The process uses a commercial porous carbon material as a matrix for absorbing the metal salt precursor. The metal catalyst is embedded inside of the carbon material by the spray pyrolysis. The carbon material is mainly used as a support for metal catalyst such as platinum, silver, palladium, ruthenium, osmium, etc., which is applied for the electrochemical catalytic reaction, for example, fuel cell. The method can only have 40-60% active metal in the synthesized composite materials. Furthermore, the process employs tin-based compounds like tin chloride and tine sulfate, which is not environmentally friendly.
U.S. Pat. No. 7,094,499 (Jun. 10, 2003) discloses a method of using different carbon materials, such as carbon nanotubes, carbon fibers, graphite sheets, as a matrix for metal deposition. Following acidic solution is employed for removal of unstable sediments on the surface of the material. The prepared carbon/metal composite material is applied as the electrode materials of lithium ion batteries. However, the carbon/metal composite material can only deliver a capacity less than 400 mAh/g. Furthermore, the process involves the use of large amounts of the strong acid and the metal chloride, which are not friendly to the environmentally friendly.
U.S. Pat. No. 7,745,047 (Nov. 5, 2007) discloses a method of using micro-scaled graphene oxide sheets as a matrix for preparing various metal/metal alloys carbon composite electrodes by a solid ball milling method, a chemical vapor deposition method or a filtered stack way. The metal/alloy carbon composite are composed by silicon, germanium, tin, lead, bismuth, aluminum, zinc, and the alloys thereof. Although the composite electrode has good electrochemical performance on the lithium ion battery, the composite electrode needs large amounts of graphene oxide as the raw material. Besides, the technique for preparation of graphene oxide disclosed in U.S. Pat. No. 2,798,878 (Jul. 19, 1954) is difficult for mass producing graphene oxide, which may limit the practical uses.
Cheng et al. (Cheng M Y, Hwang C L, Pan C J, Cheng J H, Ye Y S, Rick J F and Hwang B J, Facile synthesis of SnO2-embodded carbon nanomaterials via glucose-mediated oxidation of Sn particles, J. Mater. Chem., 2011, 21, 10705-10710) disclose a method directly use glucose and metallic tin as the precursors to prepare well-dispersed nano-scale tin dioxide/carbon composite as the anode materials of the lithium-ion battery. Cheng et al. note that the micro-scale tin particles are oxidized by the glucose molecules to form tin dioxide nanoparticles of averaged size of 2˜5 nm uniformly embedded in the carbon matrix. The nano-scaled tin dioxide/carbon composite is able to deliver a capacity of 521 mAh/g as the Li-ion battery anodes. However, the low degree of graphitization for the carbon matrix limited by the low-melting-point tin, produced by thermal reduction of tin oxide by carbon matrix, needs to be further improved a better way to confine the reduced tin in the carbon matrix is needed.
In summary, an efficient and green method for the Li-ion battery anode of good electrochemical performance and high endurance life is still challenging nowadays. Furthermore the method is needed to satisfy the industrial aspect for possible mass production.
It is therefore attempted by the applicants to deal with the above situation encountered in the prior art.